text:
What is the difference between LNAV/VNAV and LPV minimums on an RNAV approach?
This approach shows two sets of minimums that both have vertical guidance with a Decision Altitude (DA).  What is the difference between LNAV/VNAV and LPV, and why does LPV have lower minimums?

There's an FAA paper on RNAV approaches that explains the differences between LP, LPV, LNAV and LNAV/RNAV approaches. I made a table for my own reference but since StackExchange doesn't allow tables (AFAIK) here's a summary:

LP: no vertical guidance; WAAS required; MDA for minimums
LPV: vertical guidance; WAAS required; DA for minimums
LNAV: no vertical guidance; WAAS not required; MDA for minimums; requires RAIM integrity if WAAS is not available
LNAV/VNAV: vertical guidance; WAAS or baro-VNAV required; DA for minimums; requires RAIM integrity if WAAS is not available (i.e. if using baro-VNAV); possible temperature restrictions if using baro-VNAV

The difference between LPV and LNAV/VNAV is that although they both have vertical guidance, LPV was intentionally designed to be very similar to an ILS approach with an increasingly sensitive glideslope whereas LNAV/VNAV was not. Other answers have additional comments about LNAV/VNAV having been designed earlier and for different equipment which would certainly make sense.

The difference in required equipment is the reason why LPV approaches can have lower minima. GPS with WAAS (needed for LPV) provides true altitude, quite precisely, and does not require any setting. On the other hand LNAV/VNAV can be flown on barometric altimeter only and that requires setting and even when set properly has systemic temperature-dependent error, so it is not as reliable and consequently the decision altitude has to be higher.

@Jobuck I just saw that your answer was converted to a comment, whcih is why it popped up again for me. Apologies for repeating the same points again.

LNAV/VNAV approaches were originally designed for larger, more sophisticated turbine aircraft utilizing onboard Flight Management Systems (FMS). These types of approaches uses barometric altimeters and ground radio equipment to compute a descent path and add vertical guidance to an existing non-precision approach.
An LPV approach still provides vertical guidance but is not a precision approach. In this type of approach WAAS GPS satellite and ground-based data are used to provide the aircraft with the vertical descent information.
Usually a WAAS approved GPS navigator, like the Garmin 430w, is capable of flying both LPV and LNAV/VNAV approaches.

When you say that LNAV/VNAV was "originally designed for..." does this mean that they are now being used by smaller airplanes too?

@Lnafziger, if a smaller plane is equipped with a WAAS GPS, then yes, they could fly the LNAV/VNAV approach as well, but generally, a WAAS GPS would qualify them to also fly an LPV which provides a lower minimum and would be the likely choice as a preferred approach. If there is not an LPV available then and LNAV/VNAV could be flown. An aircraft equipped for LNAV/VNAV most likely could not fly an LPV.

Got it, but are there GPS's for smaller airplanes (like maybe the G1000 or similar advanced cockpits) that can do LNAV/VNAV approaches?

Yes! Certain G1000 systems are WAAS capable and can fly both LPV and LNAV/VNAV. Also the Garmin 430W/530W and GTN series of GPS navigators for general aviation would qualify. Any small airplane with a WAAS GPS should be able to fly LNAV/VNAV, but probably would never need to since they would fly the LPV instead.

Good info, but I'm not being clear!  Are there any IFR certified Non-WAAS GPS receivers in common use in light airplanes today that are capable of LNAV/VNAV approaches?

I don't know the answer to that, but I would guess no. A barometric altimeter and an FMS are usually required and not too many light general aviation aircraft are equipped with such expensive equipment. One could certainty modify a Cessna 172 to comply, but I can't think of any aircraft that came from the factory with the necessary avionics.

Hmmm, I don't know for sure, but I would think that an advanced GPS like that would be just as capable (if not more so) than an older FMS.  And almost all light airplanes today have a barometric altimeter, it's just whether or not it is encoding and can share that info with the GPS...  I'll look into it some later, thanks for the info!

Ahh, this whole time I've been meant Radar not barometric altimeter. I need to update the original answer.

Actually, I'm pretty sure that you were right in the first place and that is uses a barometric altimeter input.  Radar altimeters don't measure altitude above the runway because of varied terrain and obstacles below the approach path.

That's right. Its called Baro-vnav and here's the Advisory Circular with guidance for operators conduction approaches.
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2090-105.pdf

LPV is a higher precision approach requiring equipment beyond what is needed for LNAV/VNAV. In particular you need dual WAAS recievers in a certified installation. The improved guidance is what allows the lower DH. See this link for more information.

Are dual receivers really required?  I haven't heard that before, do you have a reference to a regulation or something that says that?

Any update? I've never seen a dual nav requirement for LPV either.

. A LPV approach can provide WAAS vertical guidance as low as 200 feet AGL.
LNAV/VNAV approaches also provide approved vertical guidance and existed
before the WAAS system was certified. At that time, only aircraft equipped with
a flight management system (FMS) and certified baro-VNAV systems could use
the LNAV/VNAV minimums.
Also the design of an LPV approach incorporates angular guidance with increasing sensitivity
as an aircraft gets closer to the runway. (This is intentional to aid
pilots in transferring their ILS flying skills to LPV approaches).
http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/library/factsheets/media/RNAV_QFacts_final_06122012.pdf

LPV - Localizer Performance with Vertical Guidance is some kind of enhanced satellite navigation with an required accuracy of 16 meters in the horizontal and 20 meters in the vertical plane during 95 percent of the time, achieved by multiple special GPS (WAAS) receivers.  Obviously this accuracy allows to reduce the minima on the approaches.

In order to get the LPV minima you need:
1 - An approach certified SBAS/WAAS capable receiver
2 - That the GPS+SBAS signals are good enough for LPV approach (horizontal and vertical protection levels low enough)
If you have an approach certified GPS receiver without WAAS, then no LPV/LP for you, but there are still the possibility of getting a VNAV or a pure LNAV approach depending on your installation and GPS signal quality.
In essence you will always automatically get the best minima possible. The receiver will tell you which one automatically.
Look up the documentation for your GPS receiver.
Dual receveivers are NOT required !
There is also the possibility of getting an LPV, but with a higher DH/same visibility if the signal quality is within LPV250 but outside LPV requirements.

Read below with a grain of salt, as I'm not a CFII.
From what I understand, there are no "precision" GPS approaches, aside from CAT1,2,3.
LPV is more accurate, uses WAAS, and means LP with vertical guidance.
LNAV/VNAV is an older tech, and was originally designed before WAAS was available. Before WAAS, aircraft with flight management/director systems were equipped to fly LNAV/VNAV. The VNAV portion consisted of Baro-VNAV equipment requirements. Nowadays, you can buy some newer aircraft equipped with Baro-VNAV, or fly those approaches with capable WAAS GPS.
Either way, you should read your aircraft manual and check it's equipment and what approaches it's qualified for.
Here's a link to more info I found.

LPV is precision and is comparable to ILS in terms of minimums.


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Is there a radio frequency that is sure to be quiet?
When flying in beautiful VFR weather, I often search for a quiet frequency so I don't listen to a lot of chatter.
Guard (121.5) sometimes works, but sometimes has "Guard"-ians on it.
("Yer on gaaard")
Many frequencies end up being a distant CTAF that have garbled transmissions.
Short of turning my radio completely off, is there a frequency within the US (or even an ARTCC) that will always be silent, but can easily swap back to a working frequency?

Some have suggested just turning the volume down and back up.
That is functional, but not quite as easy as pressing the XFER button, since the volume may be too loud or too soft after adjusting it.
I like the idea of trying the low-power frequencies that I'm less likely to hear; but I am ultimately hoping to learn of a frequency marked "do not transmit on".

Uhm .. turn down the volume of your radio?

The best choice would depend on what frequencies are in use in your area.

You mean you don't always monitor 121.5 as required by NOTAM? ;-)

J: If I turn down my volume, I have to turn it back up again, and it may be too loud or too quiet; I'm picky about getting the volume just right.  F: while I can always find a quiet frequency with enough searching, I'm hoping there is some reserved frequency that always works, regardless of area, then I can just swap it in/out with a single press of the SWAP/XFER button.

Turn off the radio?

A frequency marked 'do not transmit on' made me think of a sign I saw once on a door, which said This door must remain closed at all times.  I wondered "Then why have a door there?"

May someone explain what is the "guardians" thing on 121.5?

@Caterpillaraoz: https://forums.jetcareers.com/threads/yer-on-guard.204601/

@abelenky: tnks :)

I have down-voted this question because I feel it is poor airmanship to intentionally remove the possibility of communicating with another aircraft or ground facility.

I consider that an inappropriate downvote: There is nothing wrong with the question, you just don't like idea; but downvotes are for literally bad questions.  There are plenty of cases where it is appropriate to have a quiet cockpit;  During flight instruction, it is common for the instructor to silence the radio for the student's benefit.

When giving instruction, I normally turn the radio to the local approach facility, and turn the volume down, but not off.  While the radio noise is a distraction, students need to learn to deal with it, and need to learn to pick out calls.  The local approach frequency is then already in the radio if there were an emergency, or sometimes if we hear ourselves being called as traffic. Having it on, helps develop situational awareness.

@abelenky downvotes are for whatever reason the downvoter thinks appropiate, if the community disagrees it will even out.

Upvoted for "weirdest question ever"-- "what frequency can I tune my radio to, so that it will not behave like a radio?"  (No, kidding, sort of.  I do get the point of why the OP wants to do this.)

From the document referenced by mongo,

Frequencies (MHz): 121.425 - 121.475Use: Band Protection for 121.5
  Frequencies (MHz): 121.525 - 121.575Use: Band Protection for 121.5

It seems that these frequencies exist only to be silent space around Guard/121.5.
No one should transmit on them, and you should probably hear total silence there.
I think these are an excellent place to look for quiet space.

You might want to check out this list of assigned frequencies. These look like good bets.

136.100          Reserved for future unicom or automatic weather observation stations
122.975          Unicom (high altitude)/U.S. Forest Service air operations
123.125          U.S. Air Force NAVAID flight check/NASA T-38 Interplane Nationwide

@mongo I think that the list is just copied from the AC you referred to below. The AC is the more definitive source.

The FCC publishes the frequency assignments for aeronautical radio usage (Part 87).  You may wish to "listen" anywhere, but technically one should be monitoring guard when a receiver is available.
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC90-50D.pdf
https://www.gpo.gov/fdsys/pkg/CFR-2016-title47-vol5/xml/CFR-2016-title47-vol5-sec87-173.xml
Addendum #1  Protected frequencies, such as around guard, are implemented as "channels" which are effectively wider.  From a practical standpoint, this allows "weaker" signals to be heard without splatter or bleed over from adjacent channels.  In the case of guard, a time honored technique is to tune a radio off channel, and use that as a metric of how strong a signal is.  This is helpful if flying a grid, looking for an ELT, as an example. I have never been in CAP, but I have located several downed aircraft, and participated in one manner or another of helping locate perhaps dozens of others over the years. If you want to practice the technique, you can use some continuous transmitter, such as AWOS.  Newer radios have better off channel rejection than some of the radios which have been retired in recent years because they did not accommodate current channelization. So this technique may not yield the same information about the strength that an oder radio might. Nonetheless, knowledge of this method may prove helpful at some time.
And about all those downed aircraft? A large number of them were not crashes but rather planes tied down, and where no one apparently listened on 121.5 after that last hard landing. Higher flying aircraft would pick up an ELT, and advise center or in ancient times, FSS. They in turn would request aircraft in the vicinity to report whether they heard an ELT, and create a most probable map of where the ELT was. Most of the time,  would find ELTs at night sitting on the ground at an unlit grass field, with a mercury vapor light nearby, lighting the aircraft.
Addendum #2: To answer the OP question more directly, tune to 121.475.  If you hear anything there, you might go to 121.5 because there is likely a strong signal on 121.5. It could be a downed aircraft in your vicinity, or it could be a plane intercepting you, or something else possibly worthy of your attention. But this adjacent channel should be quiet most of the time, and should satisfy your need for a quiet frequency.

I'd try 121.1 to 121.4. I am not aware of them having been assigned for routine use. There's no guarantee that an unassigned frequency won't be in use by someone, authorized or not.
Use of frequencies between 121 and 122 are typically limited to 'low power' or other restricted applications to avoid adjacent channel interference with Guard.  This is why ground control frequencies are normally between 121.6 and 121.9.

KAVL's CTAF is 121.1

@SteveKuo I'm not surprised. There are exceptions. Frequency assignment is a complicated engineering process. There are guidelines, but sometimes there has to be an exception. If you're looking for more info, try the FAA Spectrum Plan or Regs and Procedures.

Using that Spectrum Plan as a guide, I found that 121.7750 is for Search and Rescue Practice on ELTs, so is probably pretty unlikely to hear anything there.  I'll try that frequency for awhile, and see if that is accurate.

@Gerry is correct about guard, in that it is given a 100kHz protection around 121.5.

@Gerry, perhaps you can share why you say that 121 and 122 frequencies are "low power".  The avionics tech at the local FAA facility says that the ground  and clearance delivery frequencies are the same transceiver modules used for tower and approach.  Furthermore, I am aware of no aircraft transmitter which transmits with less power on 121 to 122.  So both the ground and the aircraft transmit with normal full power on those frequencies.  There is of course a limited range due to the transmitters not being airborne, and of course, generally aircraft will not be transmitting airborne gnd freq.

@mongo  You are probably correct.  I may have misused 'low power' in trying to describe the limitations placed on the protected frequencies.  As you state, using the frequencies for ground control and similar applications effectively limits the range to near the airport where the need for 121.5 is much less.

@Gerry I think the point of GND frequencies is that they are generally used on the ground, which limits their radiated area. The need for 121.5 near the airport remains the same as elsewhere, but 121.5 is given 100 kHz spacing.  I don't have a modern transceiver rejection for 100 kHz off, but it's probably something like -95 to -105db.  It is that rejection which protects 121.5.

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Why would ASOS have a caution for Low Density Altitude?
I did my initial training in a high altitude area, where it got pretty hot in the summer,  so I'm not at all surprised when I hear an ASOS announce:

Caution: Density Altitude (a few thousand above field elev.)

But recently, I was flying in SE. Kansas when it was extremely cold outside. The ASOS announced:

Caution: Density Altitude minus 1800 ft

I understand that cold winter air can make the air extremely dense, leading to a negative density altitude. But I don't understand the caution part of it.
As far as I'm aware, low density altitudes mean your engine generates more power, and your wings generate more lift. Everything is better with low density altitudes, right?
What is the caution for?  What should I be looking out for?

Low density altitudes mean your engine generates more power, and your wings generate more lift. Everything is better with low density altitudes, right?

The potential danger in low density altitudes is that your engine generates more power than it can handle. Even without exceeding the maximum rated RPM and manifold pressure, you can exceed the rated power of an engine under low density altitude conditions.
At low temperatures the air becomes denser. At standard sea level conditions air has a temperature of 15 degrees Celcius and a density of 1.225 kg per cubic meter.
When the temperature is -30 degrees Celcius, the density increases to 1.452 kg per cubic meter. The equivalent altitude where this density is found under standard atmosphere conditions would be about -5900 ft. This is called the density altitude.
When air with these properties enters the combustion chamber of your engine and is combusted to the normal exhaust temperature it expands (increases in pressure) far more that air normally would, resulting in excessive power.
This FAA paper on Winter Flying Tips says the following about the risks associated with low density altitudes:

Do not overboost supercharged engines. This is easy to do because at very low density altitude, the engine "thinks" it is operating as much as 8,000 feet below sea level in certain situations. Care should be exercised in operating normally aspirated engines. Power output increases at about 1% for each ten degrees of temperature below that of standard air. At -40 degree F, an engine will develop 10 percent more than rated power even though RPM and MP limits are not exceeded.

Actually, manifold pressure probably would get exceeded, right? I mean, DA is essentially pressure, which means your engine would reach max MAP earlier than it normally would.

Since the temperature is very low, the density altitude is much lower than the pressure altitude. DA is not pressure under these circumstances. You can have sea level pressure with temperatures below 30 degrees Celcius, resulting in a density altitude of -6000 ft.

Right, brain fart. :)

Actually, I've been thinking more on this. I'm still not sure that's quite right; if the air is denser than standard, then your manifold pressure should rise accordingly. It's the exact opposite of why engines are robbed of power at high density altitudes - it's not that they are at the same MAP and somehow producing less power; they are actually never reaching the MAP they would if conditions were ISA... right? I feel like I'm missing or forgetting something, and googling like crazy, but not finding good resources.

Ok, I think I found a Lycoming SB that answers a couple of questions I had about overboost. Looks like 'full' power can be reached with non-redline-MAP power settings! Thanks for the response, led me to some interesting research.

@DeltaLima great answer, but it'd be even better if you included links to further reading (the Lycoming SB or anything else which helps explain your point) in the answer so that sort of thing doesn't get buried in the comments trail... simply a suggestion.

@BretCopeland. Thanks for the suggestion. It's way past midnight here so I will call it a day and expand on my answer tomorrow.

This is now a kick-ass answer (it was great before). Really nice work!

The caution is probably the default prefix for a nonstandard DA notice, not anything particular to the fact that it's negative. You're correct that lower DA will improve performance, and an FAAsafety.gov document on density altitude (PDF) doesn't discuss low DA at all.

In addition to what DeltaLima answered, also remember that denser air means the isobars are closer together and that in turn means that if your altimeter reads correctly on the ground, the same baro-altitude gives you less clearance from terrain. Some instrument procedures have minimal temperature for this reason.

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Is this plane landing or departing?
I have a picture of Air Force One I took fairly up close several years ago.

Unfortunately, I don't remember if that was on arrival or departure.
Is there anything visible in the airplane's configuration (flaps, angle of gear?) that would indicate if this is arrival or departure?

What airport was this at, and do you know from what vantage point you took the picture? Looks like it may be fairly easy to determine what runway it was touching down or taking off from judging by the GA aircraft/hangers in the background. Should tell you what end of the runway you are looking at.

@RonBeyer:  I do have that info, and I think that confirms the answer.  But the point of the question was to examine the airplane configuration, not the landmarks.

Looking at the rear wheels, it looks like they're quite angled, suggesting it's just before touch down to me. I'd expect them to be more level just after take off.

Hey now, this isn't Puzzling.SE!

@fooot Agreed!  If you know the answer, put us out of our misery!  (I'm teasing, to be clear, but I would like to know who is right ;).

The airport is KBFI, and I'm pretty sure I was standing on a ramp between A-9 and A-10 (south end of the airport).  The hangers visible have green roofs visible here, which would indicate the plane is headed north, and is Landing.

That said, I don't think there is any solid evidence based on the configuration that would indicate landing or taking off.  I was rather lucky to capture that exact moment.

Paging @Terry to the white phone. Resident 747 expert to the white courtesy phone, please.

@FreeMan Unfortunately tagging somebody in a post they haven't participated in won't show up in their notifications.

@RonBeyer, yeah, I know, but you got the reference, didn't ya'? :)

@abelenky Awwww...darn.  Well, there you go then.

@abelenky And right after you took the photo you tagged it

@FreeMan If only it did work, Terry actually flew the 742, so he'd have some insights I would imagine.

@abelenky any chance you can upload a higher-res photo for us to analyze?

Examine EXIF data from photograph and match time against landing/departure at airport?

Examining the EXIF data is not aviation related.  This is still an aviation board.

Those appear to be takeoff flaps.

More speculation: No noticeable refraction (shimmering) from hot engine exhaust. Which could mean it's landing, as the exhaust would be hotter for take-off. Maybe? Honestly, no idea. Otherwise, if shutter speed, and distance to plane and to background were known exactly, we might examine the length of the background blur to work out the speed of the plane! Eh? Eh?

So, through the answers we have 100% ascertained that the plane is either taking off or landing. Great work! ;)

@Jamiec It could have been buzzing the tower!  We did eliminate that option!

I think someone could do a greater analysis on the position of the horizontal stabilizer. Generally they are at different settings for takeoff and landing.

Landing. There is motion blur on the traffic cone suggesting that camera was moving right and slightly down. There is no blur on the plane itself since the camera was locked to the plane's motion.

Maybe we can all compromise and say it's a touch and go?

It could be a takeoff or a touch and go. If it was a landing, reverse thrust would have been deployed.

You think AF1 does Touch and Gos?  LOL.  And T.R. do not deploy until after all wheels are firmly down.

Careful - it's only Air Force One if the current president of the United States of America is onboard.  Otherwise, it's just a Boeing VC-25A.

The plane is probably taking off.  The flaps are hard to see but they don't quite look to be extended enough for landing (Looks like flaps 20).  On a 747 they extend to around 45 degrees (flaps 30, but they curve around more than that) for landing and have a huge, unmistakable profile.  Further, we know it's KBFI and we know the plane is on 31L from the photo.  Looking at the area we can deduce... (click for bigger)

...that the plane is about 3500ft into the runway proper, and 4500ft if we count the displaced threshold (and just off the ground) with the face of the southmost Jorgensen Forge building visible in the background (along with the green GA hangars).

At 3500-4000ft into the runway, hovering over the last markers in the TDZ, this seems quite late to be a landing.  It might be a very deep float, but I would expect more precision from an Air Force pilot flying the CINC around.  Air Force One is heavier empty, but probably overall lighter than a loaded 747-200 (and has powerful engines), so a 4000ft takeoff run for a light 747-200/VC-25 is sensible and probably more likely than an extremely late landing.
The flaps are more than minimum for takeoff, but seemingly less than normal for landing. Maybe 31L was running shortened that day?  Entry at B10 onto the displaced threshold would also give them an extra 1000ft - V1 just past the aim point and rotate near the end of the TDZ markers seems sensible enough.

EDIT
After running a series of simulations, it seems difficult for the VC-25 to be able to takeoff from where we see it, even when starting from B10. The VC-25 is 525,000lbs empty.  With only 100,000lbs load (fuel+people) it can takeoff by B5 at flaps 20, but only by lifting off below V2 (no wind).  This has to be a landing (confirmed by the newly discovered set of photos), but it is a very late landing indeed.
It also seems that military aircraft of the United States are exempt from the requirement to execute a missed approach in the case that they can't make the landing within the TDZ by DA/DH (using "normal" maneuvers), so perhaps the pilot just didn't care and bobbled it in anyway.  The plane did touch down in the TDZ, but just barely.

The only real problem with this answer is that...it's kind of inconclusive.  I mean, you've shown that it could be a takeoff (and I would agree, it's what I put in my answer too), but at the same time...what's to say the pilot didn't just have a bad approach and ended up floating the landing a bit?  They would still have around 9,000ft to stop in, which should  be more than enough...  Establishing the location only makes it seem like it could still go either way.

The funny thing is, after we have figured out where the plane is, the community still has a dispute about whether it is takeoff or landing.

@JayCarr I guess it is a bit inconclusive.  Looking at the photo again, it could be that the flaps are at full - it's really hard to tell from the angle and lighting. There's no smoke, so it would be a deep float if it was a landing - and the plane is nearly at the halfway point down the runway.  Touchdown at this point would leave about 6000ft of runway to complete the landing.  It's really quite late, but maybe HRH Obama likes a soft landing, lol.

@kevin This is slowly turning into the "blue dress" of Aviation.SE.  Starting to wonder if it should be closed as "primarily opinion based"....  But I'm having too much fun to do such a thing :D.

@J... I do think your answer is important though.  I was starting to go in the "it must be landing" direction until you pointed out taxiway B10 as being a legitimate place to start a roll from.  I also found some colloquial evidence on Airliners.net that say an empty 747-200 can easily get off the ground in 4000' so...this at least makes the takeoff theory plausible.

Also the angle of attack seems a bit high for landing.

@JayCarr I have seen a 747-200 take only 3300 ft to be airborne and 4000ft pulling up the landing gear. But also I have seen the same aircraft take further to touch its wheels on the ground when it has an unexpected tail wind.

So...abelensky found the series of photo this was taken from, see for yourself: https://drive.google.com/file/d/0BxQOwrukppp5WTlfaEFLTVNzTnc/view ...it's clearly landing.  I guess the pilot did end up floating it pretty bad that day ;).

@JayCarr Yeah, after running the simulations it's actually surprisingly hard to find a way that the VC-25 could take off this quickly, even from B10.  That's a really late float, though... surprised he didn't go around.  The VC-25 is 525k lbs empty - with 25klbs fuel in the tank the minimum allowed runway length is 6000ft.  That's not a lot of margin.

It's always possible that it has uprated brakes or tires versus the civilian 742.  And if it has better engines with better thrust reverse...  I dunno.  I think that, for security concerns, they would be really interested in making it so it can take off and land in a short distance and, possible, on rough(ish) terrain.  But again...I don't really know.

Don't know if you're right or wrong, by you get my +1 for a very thorough analysis!

It is blowing my mind how many people are voting for an answer that is demonstrably incorrect :P.  It is good analysis though, and the pictures are cool, so there's that too....

This answer conjures another question up: What is this strange aircraft without wings?

@mins Are you kidding?  It's a propane tank, lol.

How did you know what airport it was in?

@Cunningham'sLawyer OP noted it in a comment to the question.

@J... Oh yeah. Didn't notice that

It could be going around

going around or doing a low flyby for the cameras. Or testing approach equipment and never intending to land. Or doing touch and goes. As said already, no operational pilot for the aircraft would leave a touchdown that late.

The nose is 2,920 ft from the end of the runway see my answer. I did a detailed analysis of the line of sight from where the photographer was standing and agree with your placement of the plane.

for those unable to access the image via @JayCarr's link, click here: https://i.sstatic.net/QTrv2.jpg

Please skip to the edit after the picture to see my actual answer.  I'm leaving my original answer intact though, since other answers have referenced it.

I'm guessing that's it's taking off because:

The wheels appear to be spinning (though the picture is kinda grainy so...)
There isn't any smoke behind the tires, even though it would have just touched down.
The nose angle looks a little high for a landing.
The flaps look like they are set for take off.

For reference, here is a 747 landing.  You'll note the flaps are extended much further:

Image pulled from this youtube video, Copyright Robin Johansson
So, yeah...  I'd say it was taking off.

EDIT--  I've had a long hard think about it and I've come to this conclusion:  It can't be determined if the plane is taking off or landing from the picture.
Why?  Well, let's examine the evidence...
Landing:

Tires -- Either they just made contact and haven't produced any smoke yet, or, they pilot managed to land it so gently that there's simply no smoke.
Flaps -- They don't look fully extended to me, but it's very hard to see the inboard flaps, and it's completely possible they are fully extended
Location -- Yes, as J... established, it's roughly 4000 ft down the runway.  But perhaps the pilot was just having a bay day and floated it a bit.  There's 6000 ft of runway left, they can still stop.
Nose Angle -- As fooot pointed out, it's entirely possible the nose is high because the plane is being flared.

Taking Off

Tires -- They wouldn't be smoking because they are being lifted off the ground.
Flaps -- They are definitely beyond Flaps 10 (normal configuration) but they may have them at Flaps 20 (which is an alternate procedure, from what I've read.)  This actually reduces take off speed by 7 knots if, for some reason you want to get off the ground quickly.  Which leads to:
Location -- If the plane is mostly empty (no press, just a couple people) and it's configured to Flaps 20, it's entirely possible to get off the ground in 4000', sometimes less.  (I need a citation, I came across this doing a bunch of research last night, I swear!)  If you combine that with J...'s idea that perhaps the plane entered at taxiway B10, then the plane could easily get off the ground by the time it reach that location if it is in the configuration I've described (Flaps 20, lightly loaded).
Nose Angle -- Well, it looks to me like it's angling up for lift.  But again, this can go either way.

Conclusion:  Seriously folks, this can go in either direction.  This has basically become the "Blue Dress" of Aviation.SE.  You can't easily tell if it's taking off or landing from the picture.  Now, if someone else who was there that day could show up...maybe with weight and balance numbers...and some idea of how quickly Air Force One may have wanted to take off...maybe a grainy sound recording from the grassy knoll...and maybe a full video, verified by an independent panel of plane watches, the FAA, The Air Force, and the NTSB...  Then we'd know ;).
But as it stands, it simply isn't possible to tell.

The picture appears to be well within the height when they would be expected to flare for a landing, which would bring the nose higher.

"There isn't any smoke behind the tires, even though it would have just touched down." - No, it wouldn't. All wheels are still in the air.

@AndréStannek I disagree, it appears to me that the center, rear trucks are touching the ground.  But I'll also be the first to admit that it's hard to see.

@JayCarr now I see where you are going at. Perspective wise I was going to say it is still above the pavement in the foreground. But the actual landing strip could indeed be behind that and not visible. Hard to say...

@AndréStannek Actually, I think if you look at J...'s (frankly excellent) answer, it does a great job of establishing where the plane is.  The black pavement in the foreground is a taxiway, so I doubt it would be landing on that.  The runway itself is beyond the grass :).

I ran some XPlane simulations with a 747-400 airframe modified with the weight and engine specifications of the VC-25.  A full thrust takeoff from a B10 entry (no wind, flaps 20) can pick up off the ground short of B5 (where we see in the photo) if the total weight stays below about 625,000lbs.  A 747-400 and -200 have slightly different shapes, but really not much, so I think this is a sensible result.  A light VC-25 could do it.  Total fuel and passenger load would have to be around 100,000lbs.  That's not a lot of gas, but enough to get you somewhere.  Any headwind would naturally help.

@J... I would agree.  I've read in several places that it's more than possible for the VC-25 to do that.

"This has basically become the "Blue Dress" of Aviation.SE". Strongly disagree!. This has basically become the "Gold and white Dress" of Aviation.SE

The nose is 2,920 ft from the end of the runway proper see my answer I did a detailed analysis of the line of sight from where the photographer was standing and agree with @J... 's placement of the plane.

This picture is most likely taken during landing. The flaps configuration is the best clue. Flaps are extended more for landing than they are for takeoff. Compare with other pictures of Air Force One:
OP, brightness adjusted:

Landing (original)

Takeoff (source)

The difference in flaps is a bit subtle but seems to match landing best.

Other good clues for cases like this, but that aren't of any help here:
Spoilers or reverse thrust deployed, which will indicate a landing. The angle of the photo is bad for seeing this, and it would be a little early for them anyway.
Smoke from the tires, indicating touchdown on landing. It could be off screen, but it's also hard to tell for sure if the tires are on the ground.
Clues from other scenery in the image that will help place the aircraft at a certain point on the runway. Landings should be near a threshold, takeoffs will be further down. There isn't much to go on in the OP but with a location it may offer clues.

Based on the lighting this picture was clearly taken around mid-day. We can look at the history of recent presidential visits to the Seattle area to see when Air Force One would have been on the runway around that time.
October 2015 - AF1 arrived during the day and left in the evening. If this photo is from 2015 it would have to be a landing. However, those photos show a more hazy/overcast sky while the OP photo looks more clear.
July 2014 - AF1 arrived just after 1500 local and left in the evening again. The shadows seem to suggest that the OP photo was earlier than 1500 local (hangars still in daylight, see 2010 photos) but it would still be more plausible than a departure.
April 2014 - AF1 flew to KPAE.
November 2013 - AF1 flew to KSEA.
February 2012 - AF1 flew to KPAE.
October 2010 - AF1 flew into KBFI, looking for a good reference.
August 2010 - AF1 arrived in the evening, and left during the afternoon. If the OP is from 2010 this would support a departure. But the photo of the departure has different lighting than the OP.

Huh...see, I was thinking the exact opposite.  To me the flaps don't look like they are nearly extended enough for landing.  What makes you think they are fully extended?  (And I say this having looked at a few images already...).  Plus there's no tire smoke, even though the wheel would have just touched down...

I think it's kind of hard to tell from the lighting in the OP but I'm comparing to other photos of the 747-200, and the inboard flaps will show the most difference. I'm working on reference pics.

Does the enhanced photo not look closer to takeoff configuration than landing configuration to you?  I admit, it's extended a little bit beyond your take off picture, but the VC-25 is kinda heavier than the normal 747 I thought...it just doesn't look nearly extended enough for takeoff.

The landing photo seems to match the OP best, but it's hard to tell without a comparable takeoff angle. The outboard flaps look close but the inboard ones are much further extended for landing, which seems to match OP.

@JayCarr I don't think the VC-25 is heavier. They carry a lot less people, and the engines are very powerful for a 747 at its weight.

@kevin Actually, the VC-25 empty weight is about 150,000lbs more than a regular 747-200.  And they do carry a lot of people on it, include a few dozen press members.  Granted, it won't weight as much as a fully loaded 747-800, but it'll be pretty heavy.

But that is a problem with all of these images, we have no idea what the acutally W&B figures are on any of these planes.  And that'll have a lot to do with flap settings so....

That is true, every takeoff and landing is different, so you can't be 100% sure, but in general you expect a difference between landing and takeoff.

My only beef with your analysis is that in the take off picture, the plane is much higher off the ground (as evidenced by the angle of the shot), and that the flaps could have started retracting by then. (Says the non-pilot who isn't sure exactly when flaps go up, especially in comparison to the gear, which are clearly still extended in that image.)

@FreeMan flaps don't typically start going up until the plane has climbed out and accelerated more, it's at less than 200 feet in the frame I showed. You can watch the source video and see if it seems like the flaps move though.

@fooot I will accept your explanation and quietly go on my way... ;)

Measured directly on the image, the angle between the cheatline and the runway is 5.5°; the true pitch angle of the plane will be slightly less than that, because of a little perspective foreshortening.
According to this document from Boeing, a typical liftoff attitude for a 747-400 is 10°. (The VC-25 in the picture is a modified 747-200, but none of the various aircraft in Boeing's diagram show a liftoff attitude of less than 7°).
Furthermore, the recommended rotation rate is 2 to 3 degrees per second, so if this image shows a departure, we must be looking at a moment only about two seconds after rotation was initiated.
Since the aircraft in the picture is definitely airborne (no matter which part of the picture is the runway, it is unmistakable that none of the main gear bogies have all four wheels on the ground), I conclude that it cannot be a takeoff – at least not an ordinary uneventful one.

Did you take into account the fact that the photograph isn't level? And there's very little foreshortening, because the photograph is taken from close to side-on.

@DavidRicherby: Yes, I measured the angle between the white cheatline and the runway, not between the cheatline and the edge of the photograph. The point I make about foreshortening is that 5.5° is an upper bound for the actual pitch. (Otherwise someone might complain that because of perspective we can't conclude anything from measuring on the photograph -- I'm merely pointing out that the direction in which perspective can change things is unambiguous).

Cool. I made an edit to clarify that but feel free to roll back if you think it's not useful.

very careful answer!  that is a very good clue that it is landing indeed!

So you conclude it's a shallow landing? Why would they do this? For the comfort of the people on board as shallow landing means less vertical speed on touchdown?

Why don't we actually analyze videos of Air Force One landing and taking off instead of just analyzing the pictures?
Here is a video of it taking of at Boeing Field on 13R (the same runway, but opposite direction).
Note that the B4 taxiway mark is clearly visible in the video. By counting the number of taxiway marks and comparing it to the airport chart:

Takeoff run began at the beginning of 13R
Rotation is initiated when the plane passes B5
Airborne is achieved around B7

So that makes up, well, ~75% of runway length.
Now,

Following J...'s answer, we can see the plane is somewhere
between A10 and A9 when it touches down.
We also agree that the flaps setting is more than a conventional takeoff but less than a conventional landing.
Would Air Force One add more flaps for a short-field takeoff? Unlikely. They don't carry as much passengers and cargo, they have 4 engines, each engine is more powerful than a typical B747 engine, and they have a 10,000 feet runway.
The image is either taken moments after takeoff, or a split second before touchdown.
Note that the wheels are hanging, meaning they carry no weight of the aircraft at that point. If this was a takeoff, then rotation would have been initiated somewhere near the PAPI lights, between A10 and A11. How can it accelerate to Vr within such short distance?!

Therefore, I conclude: the plane is landing with a faster-than-average approach speed and a less-than-average flap setting.

That looks like a pretty lazy takeoff, to be honest.  Same roll, but here rotation before B4 and airborne around AB https://www.youtube.com/watch?v=l4N10mXcHyI

Plus, the thing that's really making this debate kind of pointless in the end: we have no idea what the weight of the plane is in the picture, or in your video.  Sometimes it's completely full of people and equipment, sometimes it's empty because it's just being ferried.  A 747-200 can take off in 4000ft empty, but yes, it would take roughly 75% of the runway if full (and if you're being lazy, as @J... points out.)

@JayCarr I've heard Air Force One carries a lot of gear, so I doubt you can use the regular empty weight even if it's just the pilot. Anyway the plane was 2,920 ft from the end of the runway proper see my answer

The plane is landing.

the engines are running on low power setting, otherwise there would be considerable blurring visible below the rear fuselage because of the hot exhaust plumes. In this picture the blur behind the main gear is similar to that in front of the main gear, consisting of bokeh and motion blur.
looking carefully you can actually see that the left main gear (inner or outer) has already touched the runway, and there is  visible dark smoke from this obscuring the small plane on GA platform, the one (probably a Diamond or such) to the right of the Cessna with red tail. You might expect white smoke, but since it is in the shadow of the plane, it looks very dark.
The asphalt on the foreground is taxiway A. You can tell by the yellow dash line, the runway centerline is white, and the lines and gaps are considerably longer. This part of the runway 31L is about 4ft higher that twy A, so the perspective matches to this being a shot of the moment of touchdown (the location of the plane in the picture is already well established here, kudos for J... and D_Bester)

For reference, a crop of the original picture in question:

The picture below shows the kind of blur that will be visible when engine is running at T/O thrust. The perspective is not exactly the same, but distances between photographer, the plane and the building in the background are a close enough match. Image source: pexels.com

(I will add more and better pictures when I get my hands on something not as mobile as the device I'm using now)

not sure that this answer adds anything not already available, given also that the sequence of images from which the original was part of, has been found years ago: https://aviation.stackexchange.com/questions/34586/is-this-plane-landing-or-departing#comment88757_34609

@Federico this question does not have an accepted answer, and in addition to that mine gives new indisputable pieces evidence (this being the internet does not mean anyone has to accept them) that show the plane is landing. The pictures you are referring to are not available anymore, and hiding the answer into a comment does not seem to be fair anyway ;)

The task in this question is to analyze the photo, and conclude whether the plane is landing or taking off. Most of the aswers as they stand are not clearly stating either, as they lack definitive evidence on which to base the conclusion.

I agree that the answer should be not hidden in a comment, but I do not agree with your statement that the photos are not available, I just downloaded them again. I agree that you add new points, sorry, I though that they got already discussed, since they did not sound new to me.

@Federico the link in your comment leads to a comment with a broken link. I still get a message saying the user has moved the file to recycle bin. After the comment with the link (to the rest of the photos?) There is still discussion how this cannot be a landing, which it actually turns out to be.

can't replicate. If I click on https://drive.google.com/file/d/0BxQOwrukppp5WTlfaEFLTVNzTnc/view I get to an image also in private mode with cache deleted. anyway, added a comment with a new link

Don't be fooled by the black line which looks like that the plane is on the ground.

The runway is marked with a white line, so the plane is still 3+ m in the air.
So I think it's landing.

It really isn't.  The wheels would not be level if it were in the air (the most reword trucks are level).  You are looking at the taxiway, you can tell because there is an orange cone on it, and it's clearly nearer to the person taking the photo.

Further, even if the plane were 3 meters in the air, it would have to be 3 m in the air on both takeoff and landing...so I don't follow your logic.

@JayCarr the wheels aren't level...

but you have stated in your answer that "There isn't any smoke behind the tires, even though it would have just touched down." So i need to argue

@Notts90 The portside wheels look like they are level, see the little black bump between the starboard side wheels?  I fully admit, I may not be seeing this right...

Though I will also point out, the wheels on the starboard side do appear to at least be "leveling" though they are not yet level.

You can see the shadow on the ground underneath the plane, but nowhere in the foreground of the picture, so that suggests it is above the pavement directly under the plane, not the pavement in the foreground. Besides, the foreground looks a lot more like a taxiway with the yellow stripe.

@JayCarr The wheels aren't level. Look at this photo of a 747-200 that's definitely in the air. You see that the outboard bogies are at a very steep angle, and the inboards are at a much more gentle angle (almost parallel to the plane's long axis), just like the photo in the question. (In the question photo, the right outboard is clearly separated; the left outboard and the inboards are all on top of each other but you can figure out which is which.)

@DavidRicherby What can I say, I still disagree?  I understand that the central gear are at a gentler angle (it's in the picture in my own post), but they look like the are touching the ground and, to me, it looks like the port side central truck is level.  Again, this is just how it looks to me...

@JayCarr OK, but you agree that the plane is black and gold, right? :-D

@DavidRicherby It's BLUE!  I swear it's blue!!! ;)

-1 because you state the the airplane is +3 m off the ground and therefore it is landing. Guess what: it is also 3m in the air after take-off

I can conclusively say the nose of the plane was about 2920 feet from the end of the runway proper (not including the extended area).
Notice the second door of the middle hangar lines up with the nose of the plane. To see where the next building starts just look at the roof line.

Here's my line of sight from the photographer lined up with the doors of the second hangar.

Here's the measurement using google maps

This agrees with the placement of the plane as described by J...

That is pretty impressive.   I do know exactly where I was when I took the picture, and your red line, pointing to the hanger by Helicopters Northwest is extremely accurate!  Congrats. :)

The absence of any smoke from the tires is reason #1 to suspect takeoff.
The flaps definitely aren't fully extended, but they're extended more than the minimum for takeoff.  This means that more analysis has to happen before taking the position of the flaps as definitive:
If the runway is short, both takeoff and landing would have more flaps than if it were long, and the somewhat intermediate flap setting there would make sense for takeoff, not at all for landing.  If the runway is long, you'd expect a lesser flap setting for takeoff, and the flaps shown might be reasonable for landing. Don't know what their practice is to always land full flaps or not.
Given the GA hangars in the background, I'll go out on a limb and guess that the runway isn't 10,000' long, and thus the flap setting is more appropriate for a short-field takeoff, rather than this being landing on a long runway.
Beyond that, the absence of spoilers isn't definitive, they take some amount of time to extend upon touchdown. Likewise, reverse thrust deployment wouldn't occur until the aircraft is definitely on the ground, so its absence in the photo doesn't drive any conclusion either way.
My best thought is, it's a takeoff.

The GA planes don't imply runway length, as there may be more than one runway on the airport.

The OP stated he took the picture at KBFI, and so it must be 13R, which actually is 10,000 feet. The other runway is only usable by aircraft weighing 12,500 pounds or less, which excludes a 747...

Actually, I believe the runway is 31L (same runway, opposite direction)


text:
What is the origin for "squawk" having two different meanings in aviation?
In Aviation, a "Squawk code" is a common term for a "Transponder Code".
"Squawk 2345 and Ident"
But it is also commonly a way to report problems with an airplane.
"After I landed, I Squawk'd the broken ADF, and marked it INOP"
Do these two terms share a common history?  Is it purely coincidence that the same term is used for such different meanings?

Not 100% sure but I'm pretty sure they both origin back to how a bird "squawks". Birds squawk when they fly and they squawk when they are injured. That's the only commonality I can see...

It may also have origins related to the poem The Kicker - Josh Billings c.1870 that spawned the American idiom "The squeaky wheel gets the grease"...

To be honest I have never heard squawk being used as in the latter example. It's certainly not common around where I'm from

If no one here knows, english.SE would be a good place to ask; etymology is one of their things

@J.Hougaard It's common usage in most of the USA: The list of inoperative things on an aircraft is typically called the "squawk list", and the forms used to report inoperative equipment are "squawk forms" -- This may not be true outside the USA though.

This is an interesting topic. I did some googling and found that Iran Air Flight 655 was shot down, following an incorrectly interpreted Squawk Code. So I'm guessing the 2nd usage is very significant.

According to Wikipedia (which has cited sources), the transponder usage comes from...

The use of the word "squawk" comes from the system's origin in the
  World War II identification, friend or foe (IFF) system, which was
  code-named "Parrot".

As for the maintenance reference, one of the accepted definitions is

To inform

or

To report an infraction

It may just be coincidence that they are used as they are.

I was in the USAF 77 - 81 and the term Squawk was used by maintenance troops to describe pilot complaints about the aircraft. Typically the A/C Crew Chief would write the pilot's "Squawks" in the left side of the form in the A/C log book Problem Statement section and then rate its significance with respect to safety of flight. Then they would troubleshoot the problem or coordinate with the other systems folks to work off the issues.
This was clearly a very well established term then, so I'm sure it was around throughout the Viet-Nam era.

Hi Scott, welcome to Aviation.SE. This looks like an interesting piece of first hand experience, but unfortunately I don't see it addressing directly the question. Could you please consider expanding your answer?


text:
What route should I fly in this lost comms scenario?
As I've studied, when a pilot faces a lost comm situation the pilot considers two things which are 'fly to altitude' and 'fly to route'.
For 'fly to route', the pilot follows or chooses the route following the orders Assigned-Vectored-Expected-Filed. It is a little hard for me to understand this concept.
For example, take a clearance like this:

555AZ is cleared to Grand Canyon Airport via DVT One departure PHX VOR
  vectors to DRAKE, Altitude 10000', Frequency 120.7, Transponder 3435

If my comms fail before I arrive at the PHX VOR how can I manage this situation? Do I have to go to Grand Canyon Airport directly? Or go to Drake and hold there?

I was hoping to provide a more meaningful answer by reviewing the actual route, but in Skyvector.com the DRAKE intersection is up by Colorado Springs.  Is this just a hypothetical random scenario, or do you have an actual route planned and want an answer specific to the situation?

Rule of thumb:  Whenever a clearance has an instruction to proceed from point X to point Y, where the path between those points is at the controller's discretion (such as vectors), and you have declared a comm failure by squawking 7600, you are to use your own judgement to proceed between those points by the most logical and reasonable path.
So if my clearance told me to expect vectors between two fixes and I now had a comm failure, I would just navigate my own way between them using whatever route keeps me clear of obstacles (probably direct), at or above the minimum charted altitude appropriate to the area (vectoring altitudes can be lower - you are expected to climb to the minimum published altitude following 7600 if it happens while on vectors).
On an arrival, if there is a comm failure on an arrival that involves radar vectors to final, you are expected to navigate yourself to the final approach course by the most reasonable and logical path, not lower than the charted altitude for the airspace you are in.
It's similar with the matter of timing; you are expected to start an approach at the last mutually confirmed or flight planned or expected time, so say if you arrive at a clearance limit early following a comm failure, you are expected to hold on your own as necessary so that you can proceed to the approach when you are supposed to.
The objective is that when the controller is notified of your comm failure when you squawked 7600, he/she will expect you to find your own way between any points that are discretionary at charted minimum altitudes, following a logical route and with timings that the controller can anticipate so the controller can route other traffic around you, confident you'll be able to avoid hill tops or tv towers on your own.
Much of the IFR rules structure is designed to ensure that an airplane with no communication capability can complete a trip maintaining its own obstacle clearance and proceeding in such a way that the controllers can anticipate where you are going with reasonable certainty.  The key thing is to maintain  a safe altitude and avoid going off in directions that make no sense to the controller as you find your way around.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What are the differences between blue airports and green ones on the low en-route chart?
As far as I know, a brown airport on the low en-route chart does not have an approach procedure but blue and green airports do. But what exactly are the differences between these colors?

From the FAA Aeronautical Chart User's Guide:

Facilities in BLUE or GREEN have an approved Instrument Approach
  Procedure and/or RADAR MINIMA published in either the FAA Terminal
  Procedures Publication or the DoD FLIPs. Those in BLUE have an
  Instrument Approach Procedure and/or RADAR MINIMA published at least
  in the High Altitude DoD FLIPs. Facilities in BROWN do not have a
  published Instrument Procedure or RADAR MINIMA.

So the green ones are in the FAA TPP but not in the DoD High Altitude FLIPs.


text:
What is a blind encoder?
As I'm studying, I found that GPS has to have 5 satellites or 4 satellites with "blind encoders" to use RAIM.
What is a blind encoder and what is its purpose?

Can you reference the source you are learning from or provide the relevant quotes from it? Because as far as I can tell, RAIM needs 5 satellites for error detection and 6 for correction and there is no way around it. Also, I am not sure what “blind-encorder” is it talking about, but there does not seem to be anything called blind encoder around GPS.

As I know, GPS knows our altitude (via blind encoder which is another point of reference for position information. Therefore we need only 4 satellite to trilaterate our position.

Closely related. I think you may be mixing some different things here: a blind encoder is usually part of an aircraft's altimeter, which has nothing to do with RAIM.

Sorry for that. So could you let me know what blind encoder is how it is used in A/C?

@MunPark GPS doesn't know your altitude. It knows the altitude of its satellites, but it has no idea what your altitude (or your position in any dimension) is. Your flight computers may know because of data from your altimeter(s), but the Global Positioning System doesn't know, as it's a transmit-only system that doesn't even know who is receiving its signals, let alone their altitudes.

A blind encoder is an altimeter that encodes pressure altitude and outputs it on a databus. They are "blind" in that they do not display data to the pilot. Most general aviation units use a parallel bus with Gillham encoding. More expensive units and air data computers use serial bus output, commonly ARINC 429.
Historically, the blind encoder existed to provide pressure altitude data to the transponder to enable Mode C reporting.
When it was proposed to use GPS as a primary means of navigation in the early 1990's, the FAA deemed that a means of ensuring the integrity of the signal was essential. The longer term solution was to establish WAAS which provided both augmentation and an integrity channel. The short term solution was to have the receivers include an internal monitor, which took on the name RAIM for Receiver Autonomous Integrity Monitor.
RAIM algorithms have evolved several times over the years. Since early GPS receivers were often single or 3 channel receivers, the use of altitude as a substitute for an additional satellite was common. (Altitude is just another range in the rho-rho computation.)
Later GPS receivers moved to 6 and 12 channel receivers, thus enabling RAIM algorithms that don't need altitude data except in extreme cases.
So yes, the number of satellites needed for a RAIM calculation can be reduced by one when pressure altitude is available from a blind encoder.

+1, I had no idea that there's a link between altitude encoding and RAIM. I'm not doubting your answer, but do you have any sources on the algorithms you mentioned?

The information is in the GPS MOPS, RTCA DO-229. The basics are covered in Appendix G—REQUIREMENTS FOR BAROMETRIC ALTIMETER AIDING in DO-229C.  I'm not sure if the reference is still valid in the current version DO-229E. I do know that the newer version does require the use of FDE RAIM as the algorithms have evolved.

thanks for that!

Of course the barometric altimeter reading depends on the weather, so the position obtained with use of barometric altitude has lower accuracy. Good enough for en-route navigation, but not for approaches or anything needing RNP.

@JanHudec  Certainly not CAT I or APV approaches, but a TSO C129 GPS with RAIM is capable of RNP 0.3 non-precision approaches. When combined with an FMS the same GPS sensors support LNAV/VNAV approaches. They did require pilot input of the local altimeter setting. Most of those approaches had MDAs in the 250 to 400 foot range.

Receiver autonomous integrity monitoring
Receiver autonomous integrity monitoring (RAIM) is a technology developed to assess the integrity of global positioning system (GPS) signals in a GPS receiver system. It is of special importance in safety-critical GPS applications, such as in aviation or marine navigation
Check out the GPS article in this FAA newsletter to start with:
http://www.faa.gov/news/safety_briefing/2010/media/JanFeb2010.pdf
RAIM prediction is what is of primary concern for Non-WAAS equipped GPSs.
If you are WAAS equipped then you are good to go without doing prediction.


text:
How does the power requirement change when weight and speed change?
Suppose I have an airplane with a certain weight M, which uses a certain amount of power P, to fly at a certain speed V.
If I use the same airplane, but quadruple the weight (4xM) and double the speed (2xV), what is the resulting need in power?
I would like to understand the physics of this, for an ideal system. We can ignore how efficiencies change with velocities, etc.
Here is my reasoning: the airplane needs four times the lift to fly in the same mode, which will be provided since the speed has doubled. The only force the engine needs to overcome is the drag, which is four times higher, i.e. the required power is 4xP, four times higher.

Short answer: No. $ P = F \cdot v$ and since $ D = \frac{1}{2}C_D\rho v^2S $ it follows that $P\propto v^3$
Let's take a more simple case: a block moves over a rough, horizontal surface in a vacuum and a force is applied such that its velocity $v$ stays constant. This force is always the same, since the "drag force" is given by the friction coefficient times the normal force. Here, the kind of relationship that you're thinking of would hold: if we're moving at $2v$, we need twice as much power ($P=F\cdot v$).
Look at a fixed distance along that trajectory: we do the same work in both cases ($v$ and $2v$), so we put in the same energy which dissipates through friction, i.e. heat. However, we now need to do the same work in half the time, so the power is double. In a certain way, it's "more difficult".
Now for an aircraft, the drag force itself is proportional to the square of the velocity. So, in conclusion, there are "two effects" which "add up": a quadrupling related to the increased force and a doubling due to the increase in velocity. Hence, the power is multiplied by 8.

Edit (in response to comments below):
Ok, let's do another thought experiment: we place a jet engine in a wind tunnel and keep it at constant thrust and constant mass flow (choked nozzle), which results in a constant velocity increment across the engine. The power contained in the jet (the airflow exiting the engine at higher speed $v_j$) is $\frac{1}{2} \dot m v_j^2$  and the power contained in the incoming flow is $\frac{1}{2} \dot m v_0^2$. The difference between the two is called the "propulsive jet power"; it's the power which is "available" from the acceleration of the flow. Now, you can see that because both terms are squared, it is not just the velocity increment which counts (as it was the case for the thrust), but also the magnitude of the two terms.
So alternatively to the "thrust power" given by
$$P_{thrust} = \dot m (v_j-v_0) v_0 = T v_0 = D v_0$$
we can also consider the "propulsive jet power"
$$P_{prop} = \frac{1}{2} \dot m (v_j^2-v_0^2)$$
where the proportionality to $v_0$ at constant thrust is maybe more clear. The difference between these two quantities is called the power loss ($P_{loss}=\frac{1}{2} \dot m (v_j-v_0)^2$) and is a measure of how much of the orginal chemical energy contained in the fuel is lost to kinetic energy in the jet.
You can see that if the velocity differential is constant, the power loss is constant. So if we have shown that the propulsive jet power is proportional to $v_0$ at constant thrust, the thrust power (which is the power that "actually moves you") must also be proportional in this way. And this proportionality is related to the fact that the kinetic energy of a mass is proportional to the square of its velocity.

Thanks Daniel! The formulas in your short answer makes total sense (and Tanner Swett has already explained it to me under a different topic). However, I have a hard time understanding it intuitively. Imagine that the aircraft is not traveling at all relative to the earth. Instead it fights wind speed (as in a wind tunnel), and we do the same thought experiment. (... more to follow)

To overcome the drag component the engine needs four times the power. The wind speed is double, but oncoming wind speed is irrelevant to how much thrust/force an ideal engine can give. Speed difference between incoming and outgoing air of the propeller is what creates thrust. So in my view there is only one component to overcome; the drag. Take away drag (vacuum) and you are in a space ship, and thrust is constant regardless of speed.

A related question: will an ideal engine/propeller create the same thrust force at the same power, regardless of incoming air speed? As far as I understand the subject, it will. Please correct me if I'm wrong!

I've added an alternative way to look at it above. Some other remarks: be careful not to mix up jet engines and propellers driven by piston engines, these work completely differently. The power of a piston engine is of course independent of the air speed, but the thrust that the propeller then produces is highly dependent on the air speed. The latter is of course also true for a jet engine as a whole.

Thanks Daniel. The first component is easy to understand for me (double speed gives double drag, which requires four times the thrust). As for the second component: do you mean that it is inherent in the design of a motor/propeller propulsion system that when the incoming airspeed doubles, it takes double power to generate the same amount of thrust? This is not easy for me to understand on a fundamental level, even though I can see that the formulas make sense. Its like saying that there is a difference in effort between walking up a moving escalator vs a stopped escalator.

It's not just inherent for an airbreathing propulsion system but it's somewhat of a physical law that at constant force, the power is propotional to $v$. I've been trying to come up with an intuitive explanation such as the one where the molecules of air are "hit with a bat" (as you've used it before), but that's quite difficult, since the behaviour of an airflow just depends on so many factors (compressibility, transonic effects, thermodynamics, energy losses etc.), so it's a bit like trying to explain $F=ma$ in a more intuitive way... I guess you've had a look at the Wiki article about power

@BjörnMorén I like the escalator analogy, but let me alter it a little bit. Suppose your goal is to remain in one place regardless of what the escalator is doing. Then it's easier to walk up a moving escalator than it is to stand still on a stopped escalator. And the faster the escalator is moving (and thus the faster you have to walk), the harder it is to walk, in order to stay in place. The force you're exerting is the same in all cases (it's equal to your weight); the only thing which makes the faster elevator harder is the speed.

Another analogy along the same lines is: it's harder to climb a ladder quickly than it is to climb a ladder slowly. (As an aside, once you get into going down a ladder, the analogy breaks down. A well-designed ladder-descending machine would gain energy from descending a ladder; but since human beings are not well-designed ladder-descending machines, we have to expend effort to descend ladders.)

Thanks Daniel and Tanner for taking the time. Yea it is still tricky to accept, even with the ladder analogy, but since it is a fact of physics, I have to stand corrected and accept it. It makes a lot of sense from the perspective of energy conservation for the system as a whole (second law of t.d.). Good to learn new things about the universe.

Let the initial state have the index 1. If drag is $D$, then $P_1$ is:
$$P_1 = D_1\cdot v\;\; \text{or} \;\;\frac{\rho}{2}\cdot v^3\cdot S_{ref}\cdot\left(c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)$$
Now, state two is:
$$M_2 = 4\cdot M_1 \;\;\text{and}\;\;v_2 = 2\cdot v_1$$
At twice the speed dynamic pressure is four times higher, so the lift coefficient $c_L$ stays unchanged. So do aspect ratio $AR$ and zero-lift drag coefficient $c_{D0}$. In this special case the term in the brackets in the first equation has not changed (if we neglect the higher Reynolds number which lets $c_{D0}$ shrink).
Power is the product of drag and speed, and drag in turn is proportional to speed squared, at least in a first order approximation. So in combination power must increase with the cube of speed if mass is quadrupled and speed doubled.
If you use other factors, the result depends where on the drag polar state 1 is, in other words, what is the ratio of zero-lift drag to induced drag. If mass is quadrupled without a change in speed, the lift coefficient will also quadruple and its square will increase by a factor of 16. If zero-lift and induced drag were equal in state 1 (that is the minimum drag polar point), now the term in the bracket grows by a factor of 8.5, and so does your power requirement.
If, however, only speed changes, the lift coefficient in state 2 will only be a quarter of that in state 1 and the drag coefficient in state 2 will be dominated by its zero-lift part. Again, if both parts were equal before, now the drag coefficient in state 2 is only 53% of its value in state 1. But since speed has doubled, the required power will now be 4.25 of that at state 1.
If you want to see how things really change (including Reynolds number effects), take a look at this answer and definitely at this one, too.

Thanks Peter. I need to study this topic more before I can grasp your explanation.

Peter, your speed change only consideration really helps illustrate one point about induced drag - the lift requirement - does not change much with increased velocity and, as you said, most drag increase comes from CDo.  The math matches a 4 fold power increase approximation.

It might be easier to break this down into 2 parts.

Thrust required to overcome increased drag at 2x speed
D is proportional to Vsquared, so 4x thrust is required, theoreticly yielding 4x lift.
Power discussion is a little more complicated, as it involves Force x distance/time or
Force x Velocity of the aircraft and/or the power output of the engine, in terms of fuel
burned per given unit of time.

Comparing doubling of speed with respect to distance shows that while the faster aircraft is more "powerful" due to increased speed and weight kg meters/second squared x meters/second = kg meters squared/seconds cubed, the difference in fuel consumed to go the same distance would be 4xthrust x 0.5 time = 2x fuel needed.
So now we need to define "power" for this application.  As far as the instantaneous state of the aircraft, it is much easier to think in terms of Forces, and yes, both piston and jet are the same here. Forget about pulleys and gears and just look at thrust.  Thrust = Drag.
A prop overcomes drag to produce thrust by burning a certain amount of fuel, just like a jet.
The real key is efficiency.  So assuming our scale-up to yield 4x thrust produces no change in efficiency, we must burn 4x more fuel, but only for half the time to go the same distance.  But the propeller is the issue.  One may attempt to keep efficiency close with a variable pitch prop, but in reality, attempting to increase thrust 4x would probably overheat the engine rather quickly even if it were possible.  Increasing weight by that magnitude would more likely involve bigger wings and more engines.
Check this out, as ton miles per gallon:
"good" mileage car         2 tons x 30 miles/gallon = 60 ton miles/gallon
60 mph
tractor trailer                   40 tons x 7 miles/gallon = 280 ton miles/gallon
 60 mph
Cessna 172 1 ton x 12 miles/gallon =  12 ton miles/gallon
110 mph
Boeing B29  65 tons × .5 miles/gallon = 32.5 ton miles/gallon
240 mph
Boeing B52 240 tons x .18 miles/gallon = 43.2 ton miles/gallon
600 mph
Boeing 747 400 tons x .20 miles/gallon = 80 ton miles/gallon
600 mph
Avro Vulcan  85 tons  x .28 miles/gallon = 23.9 ton miles/gallon
Mach 1
Concorde  185 tons x .24 miles/gallon = 44.3 ton miles/gallon
Mach 2
North American XB 70  270 tons x .16 miles/gallon = 43.4 ton miles/gallon
Mach 3
Freight train                 500 plus ton miles/gallon
Wandering albatross    12 to 20 lbs  up to 60 mph

Thanks Robert, this really makes a lot of sense from the perspective of amount of fuel (energy).

The XB-70 was the proud achievement of North American Aircraft. What an insult to attribute it to Boeing!

Oh sorry, I thought the B stands for Boeing

Yes, Bjorn  It seems V cubed more describes an object that has velocity and is accelerating, what I try to do when I hit a golf ball.  Perhaps a description of an energy state.  We do not seem to need 8 times more fuel to double our speed (thank goodness). So I wonder.


text:
Has the FAA ever granted a LODA for compensated instruction in a non-LSA E-AB?
I have been trying to find a list of granted LODAs to get this question answered. No joy. I am considering purchasing a Sling TSI E-AB. It would be great to be able to instruct in it for compensation.

This one?  https://www.airplanefactory.com/aircraft/sling-2-kit/  And this LODA?  http://fsims.faa.gov/wdocs/8900.1/v02%20air%20op%20&%20agency%20cert/chapter%2006/02_006_003.htm

From my reading of it, the LODA does not cover giving primary instruction.  But it's my first time seeing it.  I own/fly a certificated plane, and it was never a problem getting instruction in it, experimental is a new area to look into.

The odds are not in your favor. :(

You may have to contact the FAA directly to get an answer on that but it seem like an unlikely case. Since you are looking for a LODA that covers "training flights" you would need a LODA SFA

D.    LODA Special Flight Authorization (LODA SFA). A Flight Standards
  office normally issues a LODA in cases where frequent operations of a
  specific nature occur over a protracted period of time. However, there
  may be situations such as ferry flights, sales demonstration flights,
  and training flights where the 60-day requirement may not be feasible.
  For these situations, a Flight Standards office may issue a LODA SFA
  on a case-by-case basis for specific flights. A LODA SFA is a LODA
  authorizing an operator to accomplish short-term operations (normally
  a maximum of 30 days) in accordance with 14 CFR part 91, and can be
  issued for the following:

LODA SFA's are short term as discussed later on, specially they are typically 30 days in duration

...
2)    A LODA SFA is conducted in accordance with part 91 rules. The maximum duration of a LODA SFA is normally 30 days.
...

To regularly provide instruction in the aircraft you mention you would effectively have to continuously apply for a LODA SFA on a rolling basis, something the FAA likely will stop approving eventually. I would say that your use case does not really fall under the broader spirit of the regulation

...
LODAs to all of part 125 are issued for operational uniqueness
...

Although you could make a case if you were offering training to others specifically looking to buy that aircraft. If you are just looking to offer flight instruction the FAA is likely to tell you to go find an approved airframe and play by the rules. I cant find an exact price for a sling kit but Im seeing north of 100K for built ones, even if the kit costs half of that @ 50K you can get a whole lot of 172 or Cherokee 160 for that price and offer instruction without the hassle of special authorization (above whats normally needed).


text:
What is a "sidestep landing" in an instrument approach?
I have never seen a sidestep landing on an approach plate. What is a sidestep landing and when I can chose this approach?

Related

From the AIM 5-4-19:

5−4−19. Side−step Maneuver
a. ATC may authorize a standard instrument approach procedure which serves either one of parallel runways that are separated by
  1,200 feet or less followed by a straight−in landing on the adjacent
  runway.
b. Aircraft that will execute a side−step maneuver will be
  cleared for a specified approach procedure and landing on the adjacent
  parallel runway. Example, “cleared ILS runway 7 left approach,
  side−step to runway 7 right.” Pilots are expected to commence the
  side−step maneuver as soon as possible after the runway or runway
  environment is in sight. Compliance with minimum altitudes associated
  with stepdown fixes is expected even after the side−step maneuver is
  initiated.
NOTE−
Side−step minima are flown to a Minimum Descent
  Altitude (MDA) regardless of the approach authorized.
c. Landing
  minimums to the adjacent runway will be based on nonprecision criteria
  and therefore higher than the precision minimums to the primary
  runway, but will normally be lower than the published circling
  minimums.

Also, a sidestep approach should be listed on the approach plate with it's own minima, and this would typically be used where only one parallel runway has a (working) ILS but ATC prefers traffic to land on the other one(s) when possible.

It’s for flying an instrument approach to one runway, then sidestepping, or moving over to land on a parallel runway nearby
EG “Cessna one seven two Sierra Papa, you are 4 miles east of DUANE.  Turn right heading two eight zero, descend and maintain on thousand eight hundred.  Cleared ILS Runway 32L, sidestep to land Runway 32R.  Maintain one thousand eight hundred until established.  Contact Boeing Tower one two zero point six.”
A sidestep to land approach would be flown down to the published circling minimums and is considered to be a circle to land procedure.  If circling did to terrain or obstacle, etc. is not allowed, neither would a sidestep procedure.

According to the AIM, a side-step is flown to the MDA, not to circling minimums

Circling Approaches make use of an MDA.  Now the AIM does state, Now AIM 5-4-19 does state that “Landing minimums to the adjacent runway will be based on nonprecision criteria and therefore higher than the precision minimums to the primary runway, but will normally be lower than the published circling minimums“.  That being said unless specific side step minimum are published along with the plate, I’d play it safe and use circling minimums for a side step.

I guess my point was that the AIM says that side-step minima aren't the same as circling minima. I see what you mean about being conservative with altitude but using the circling minima could leave you too high to land without circling. That might not be an issue anyway, of course. I've never flown a side-step approach myself so I don't know what ATC expects in practice.

For a sidestep maneuver, not necessarily.  All that is required here is that you have the runway environment of the parallel runway to be used for landing in sight by the time you reach circling minimums.  If not, execute a go-around as you would if flying a circling approach.  What the AIM states is kind of a gray area without specific published minimums for a side step maneuver.  Without further input from an authorized source, I’d say just use circling minimums for the approach.  Anything else may be risky.

Would ATC even call it a "sidestep" approach if there aren't published minima for that, or would they call it a "circling" approach?


text:
Is there an ideal air temperature for best performance in a light aircraft?
I know cold air is better for engine performance in general, colder air is also denser making lift components stronger(from what I understand).
I was just wondering if there is a temperature or a range of temperatures that offer the best performance overall?
Is there a temp that covers all areas such as takeoff/climb performance, cruise etc. or is it something where each performance area has its own "sweet" spot?
Let's use common flight trainers like the C172 as the example.

The best horsepower listed is at -20C in the 172S POH.  I always thought the engine made full rated horsepower at sealevel, 29.92 on the barometer, and 59F (standard temperature and pressure).  I don't see anything in the POH to back that up. I don't have a separate engine book to see if if might be there.

Good Evening Alex,
just for the record I'm a Private Pilot with about 150 hours of flight time, I would recommend speaking to a Flight instructor if you have any more questions about Aircraft POF. (principles of flight and performance)
Best Performance can be narrow down to a simple formula
Best Performance = High Pressure + Low Temperatures
1 hectopascal is equal to 30ft change
1º celsius is equal to a 120ft change  br>
If you are looking for the landing and T/O I would suggest looking a Performance charts-which

Relevant https://aviation.stackexchange.com/questions/39151/is-there-a-maximum-or-minimum-temperature-for-take-off-and-landing


text:
How should one fly the entry procedure to an approach when the hold is not aligned with the outbound course?
Consider the following NDB DME approach into runway 08 at Jersey (EGJJ):

Let's assume we are coming in from the North and are currently cleared direct to the JW NDB flying inbound on a 180° track. Now we are cleared for the NDB DME approach. How should the entry into this approach be flown:

When reaching the NDB, immediately turn right to intercept the 246° outbound course. This seems to be prohibited by ICAO PANS-OPS because the difference between my inbound course and the outbound course is larger than 30°:

Unless the procedure specifies particular entry restrictions, reversal procedures shall be entered from a track within ±30° of the outbound track of the reversal procedure. However, for base turns, where the ±30° direct entry sector does not include the reciprocal of the inbound track, the entry sector is expanded to include it.

(ICAO Document 8168, Vol 1 §4, 3.3.3.1)
Enter the hold with a direct entry and immediately follow the Alternative procedure by extending the outbound leg of the hold. This seems to be the best option, but I'm not sure if this would be expected without being explicitly cleared for the alternative procedure.
Enter the hold with a direct entry and after one racetrack when crossing JW fly a course reversal / alignment turn to the left. As far as I understand, this would be the normal procedure if the hold were aligned with (or within 30° of) the outbound course since no course reversal would be required any more. But in this case, it seems weird since there is nothing in the chart about an alignment turn.
Or maybe something else?

Here is what I imagine the options 1-3 to look like:

Does this answer your question? How to properly enter a holding pattern?

@ManuH No, I know how to enter the holding pattern (direct entry in my example). The question is about how I can get from the holding pattern onto the outbound course of the procedure.

Options 1 & 2 are virtually and practically indistinguishable, and probably beyond the ability of most pilots to fly as precisely as you depict them.  (unless the autopilot was coupled to a GPS programed for the profile...)  And unless you are just building time and practicing holds I'm not sure why you would want to fly #3.  You are just burning fuel making extra laps.

I flew many of these types of approaches in northern Canada from 1980 to about 1990. In my opinion Option "2" is the best, followed by option 1, but all three are possible.
It is my understanding that when cleared for an approach, you own the airspace, and as long as you stay in the "protected" airspace, you can do almost anything you like.

That's good to know all are allowed. Could you elaborate a bit on what exactly is part of the "protected" airspace? In the first example on this page (linked under the other answer) the pilots got into trouble for violating some airspace, even though it looks similar to my option 1.

For Protected airspace" see this question and answers:  https://aviation.stackexchange.com/questions/21612/what-are-the-dimensions-of-the-protected-space-provided-by-a-holding-pattern

@Bianfable that would be the case of approaching from the south (and is a reason why what should be done when approaching from the south might be a more interesting question).

It’s very rare that I get to do a true NDB approach. Only one of the training aircraft I’ve flown had an ADF. And we had to use the GPS nearest page in lieu of DME. Using the bearing function in the G500/1000 has been a close substitute until the local NDBs started disappearing one by one.
But, the way I would interpret the IAP to include it’s notation in the upper left corner is that your #1 option is the best one if you do not have to enter the hold for any reason. You are just using the course from D8.3 to D5.3 to align yourself with the ILS since there is not an Intermediate Fix before the FAF of FQ08.
If you were to have to “go missed”, ATC could clear you go direct to JW after your right turn, to begin your next approach. This would make any hold unnecessary. It would just be another variation of your option #1.
If you had to enter the hold for any reason (such as to delay your approach, after a missed approach, descent from a higher altitude, or a hold in lieu of a procedure turn / course reversal), you would basically ignore the direct course from JW to D8.3. You would properly enter the hold for at least the first right turn of a circuit after crossing JW. Once you establish yourself on the outbound leg of the hold (completing your right turn and coming wings level), you would fly direct to D8.3. Once you cross D8.3, you can begin your approach again assuming you have been given the proper clearance before leaving the hold. This would be a slight variation of your option #2.
ATC typically does not care whether you enter the hold using the teardrop, parallel, or direct method. As long as you establish yourself on the hold by first crossing (entering at) the designated hold fix, and you stay in the protected airspace. After entering the hold at JW using the parallel method, you would be established on he hold. After entering the hold at JW using the teardrop or parallel method, you would be established after crossing JW again (the second time). This and the above variation of your option #2 would make your option #3 unnecessary.
IMHO.

If you look at the provide view of the approach plate, you'll see the normal procedure requires you to go to D8.3 IJJ, and then proceed on the inbound course of 083°.

Yes, that's clear. My questions was how do I turn onto the outbound leg to D8.3 IJJ from the NDB when arriving from a course more than 30° offset?

@Bianfable See if this page gets you close to an answer

The Isle of Man example in that document looks quite similar, but they don't explain the correct entry procedure since they say they got radar vectors instead...

@ Bianfable There is no "course reversal", only a hold for the published missed (note the thin line that depicts the hold).
PANS-OPS aren't a concern when flying within the U.S., are they?
#1 Crossing the NDB turn right 246 and intercept the charted track to IJJ.


text:
How can I calculate the fuel required for a specific route and aircraft?
Okay, I'm writing a online game. I've got two airports and the equipment. For example: Heathrow - LAX on a 744.
What I want to work out is the fuel required, as this will apply a cost to the airline. I know there are many many things such as wind, temperature, regulatory requirements like alternate airport etc but I want something simple.
How can I work out simply the fuel required? Are there charts I can use for working out takeoff, each hour in cruise and descent?

Welcome to aviation.SE! We have several questions already on calculating fuel burn: here, here, here. If you're new to the site, the [tour] may be useful.

If you just want something simple, just look up the average fuel consumption for the aircraft type (in gallons per hour), and multiply that by the duration of the flight. Although airlines have more sophisticated tools to plan refuelling, this is how GA pilots estimate how much fuel there should be in the tank.
Official fuel consumption figures can be hard to get hold of because the Pilots' Operating Handbook and other documentation for the aircraft might not be publicly available, but it's easy to find out rough figures from web forums populated by pilots of that type.
If you are interested in something more complex (and accurate), see How can I calculate the fuel consumption of an Airbus 320-200 at various loads?

Thanks; I've looked at the average consumption per hour but depending on the length of flight this will vary. For example, a 3-hour flight on a 777 will have a vastly different consumption to an average consumption on a 14-hour flight. I could look up averages for each hour and place them in a table.

Any recommendations on where to get the Breguet equation explained in an example?

@kiwis The A320 question that Dan mentions in his answer has an example of using the Breguet equation. If it isn't clear enough for what you need, you might like to ask a new question about it specifically, but please do explain exactly what you're looking for that isn't already answered. Otherwise, people will probably refer you back to the A320 question again.


text:
In India, what is the difference between "local flying area" and "airspace"?
Can anyone define what is a "local flying area" and an "airspace" and what is the difference between the two? It would be good if the definition is as per Indian rules.

Welcome to Aviation.SE, you have this question tagged as both FAA and DGCA but you are asking about Indian rules in the body. You may want to remove the FAA tags as they are a bit confusing. If you are looking for FAA answers as well you should add that to the body as you may get more answers that way.

A local flying area is airspace that is designated by local air traffic control for general flying not involving circuits and landing. In the US it is something that is loosely referred to as "the practice area." In this area aircraft can perform practice and other maneuvers, and air traffic control will be aware of it and can warn other aircraft to be on the lookout for this. In India it is common for these practice areas to be segregated for flying school aircraft, and medium to heavy aircraft.
To put it another way, all local flying areas are part of a country's airspace, but only a fraction of the airspace is designated as local flying areas. I hope this helps.


text:
Is there a standard on-board diagnostics protocol for FADEC aviation piston engines?
Almost any car engine manufactured since 1997 will have on-board diagnostics, either the OBD1 or more recently the OBD2 standard which provides a standard for protocols, standard message codes and a standard connector which is universal across all engines (there are different pinouts used but newer readers can usually read them all), plus the ability for manufacturers to add their own fault codes where applicable. There is also telemetry available from the engine sensors which can be read to diagnose engine health, for example air flow and inlet air temperature, engine coolant temperature, etc.
I am well aware that the vast majority of aviation pistons are completely mechanical, but for the small percentage of electronically controlled engines that are out there is there any such standard? Do they use OBD2, another common standard, or are they all proprietary?

"OBD2 standard which provides a standard protocol, standard messages and a standard connector which is universal across all engines" Having worked on OBD2 vehicles, I can tell you that it is not universal. Domestics have a few protocols, European cars seem to standardize on CAN (ISO15765). All told there are a lot, J1850 PWM, J1850 VPW, ISO9141-2, ISO14230-4, ISO15765-4/SAEJ2480. There are at least 2 types of "standard" connectors as well. There are "standard" PID/PGN's but they are hit or miss if they are implemented in favor of the manufacturer specific one...

OBD1 had many connectors, OBD2 has one, although there are different pinouts for it. These are well understood enough that there are readers that work with them all, and they are cheap and (relatively) easy to use. I don't think it's useful to go into detail on the protocols that are in use in my question, the point is to find out whether automotive systems are in use, or whether they use a different system.

@RonBeyer By US law, 2008+ vehicles must present a CAN interface. So it has been universal for over a decade.

@user71659, yes and no. There is a specified small set of diagnostic messages over CAN that are required for emissions and general engine health check, but that is a tiny fraction of what the vehicle actually provides, the rest being vehicle-specific using various standards as a base.

OBD systems were introduced by law in the 80s to reduce / control emissions, so it originated as a method to determine fault with emissions control systems. However, it was refined enough to monitor and control in real time engine and powertrains sytems in further iterations. Keep in mind that the OBDI / OBDII is a protocol that is run on the CANBUS network, which is important to remember that these two are separate entities  (CANBUS can run several different protocols, as Ron Beyer had stated). Other networks such as the LINbus for Audi/VW/BMW run different protocols but still work in a similar fashion.
From my military aircraft maintenance experience (from way back), our systems ran on the 1553 databus, which linked all systems together (nav, comms, AP/FD, etc) and is essentially the CANBUS equivalent. I believe Civil aircraft used the ARINC429 system, however I cannot confirm. For the protocol side, many aircraft (though mainly helicopters) use the Health Usage Monitoring System (HUMS), which provides the OBDII equivilant (more or less) to report back on engine condition, conditional maintenance, operation, etc.
So to make a short story long, there area a few standaridzed networks that aircraft use, however so far there is no standard protocol for all engines. Keep in mind that car manufacturers design and build the system as a whole in-house (chassis, powerplant and drivetrain), so it is not an issue to have all the systems integrate in a relatively simple manner), where airframes are generally designed by a company that will use a powerplant designed and built by a different manufacturer (or perhaps event the same airframe could have different engine variants from different companies), which makes standardization increasingly difficult.

Funny enough while most car manufacturers do also make the engines and drivetrains, they still outsource much of the electronic controllers, and the departments in large companies behave almost as independent companies anyway. I'd rather lean towards saying that the automotive situation is simpler because everybody at least can do CAN and because the buses used are not as crazy resilient as the ARINC429 where every transmitter transmits in a separate line so they never need to tap as many wires.